1. Field of the Invention
The present invention relates to a droplet ejection apparatus configured to eject droplets of a liquid such as ink to a recording medium and a method of controlling the apparatus. More particularly, the invention relates to a droplet ejection apparatus equipped with a post-processing mechanism configured to correct a curl of the recording medium to which the liquid is attached and to dry the liquid attached to the recording medium and a method of controlling such an apparatus.
2. Description of Related Art
There is known an ink-jet printer, as one example of a droplet ejection apparatus, configured to form an image on a recording medium by ejecting ink to a recording medium such as paper, cloth, or a film. The ink jet printer often uses water-soluble ink. The water-soluble ink contains a large amount of water as a solvent. Due to the water component contained in the ink, there may be caused a curl of the recording medium to which the ink has been attached by image formation. The state of the curl varies depending upon conditions of the attached ink. In general, when a difference in the amount of the water component becomes large between a front surface and a back surface of the recording medium due to the attachment of the ink to the recording medium, the curl is likely to occur. Where the recording medium suffers from the curl, the recording medium is not stacked in good order when discharged, causing a trouble that the recording medium is bent or placed out of position. Accordingly, it is preferable to accurately estimate or predict the state of the curl of the recording medium and to appropriately restrain the curl. In view of this, there is proposed a technique in which a liquid amount ejected by a droplet ejection apparatus to each of regions defined on the recording medium is calculated and a curl amount of the recording medium is predicted on the basis of a position of each region and the liquid amount ejected to the corresponding region. In the disclosed technique, a heat application time by a heater or a restraining time of a curl restraining mechanism for correcting the curl is increased where the amount of the curl is equal to or larger than a prescribed threshold.
In general, in an ink jet printer, ink is ejected to recording media that are successively supplied so as to form, an image thereon, and the recording media on each of which the image has been formed are sequentially discharged to an output tray so as to be stacked thereon. On this occasion, if in a state in which ink on a previously discharged recording medium is not dried yet, a following recording medium is subsequently discharged, there is caused the so-called set off in which the ink on the previously discharged recording medium is attached to the lower surface of the following recording medium. In view of this, there is proposed a technique in which a conveyance speed of a recording sheet necessary for drying the ink ejected to the recording sheet is calculated on the basis of the temperature of the vicinity of an ink-jet recording portion; and a ratio of black pixel elements in recording information, and the recording sheet is conveyed at a speed not higher than the calculated conveyance speed.